I have mixed thoughts about this one.
On the one hand, the writing style didn't work for me. For my personal taste, a little humor goes a long way, and M.J. Trow's novel reads like one extended, often tortured pun. I found the unabashed tongue-in-cheek tone to be a particularly uncomfortable fit with the subject matter, namely the Jack the Ripper murders. While I appreciated the completely different take on Sherlock Holmes and John Watson (neither of whom has much of a clue, literally or figuratively), I could never quite tell if the author was laughing with or at Lestrade, which was a bit off-putting.
(I fully realize that this is partially my fault for jumping into the middle of a book series, but I'm currently trying to go through most if not all of the Sherlock Holmes-meets-Jack-the Ripper novels, so that's the context in which I read this.)
That said, Trow can't be faulted for his attention to detail in the Ripper cases. Many of the historical prime suspects (such as Montague Druitt, Sir William Gull, Aaron Kosminski, Michael Ostrog, and "Jill the Ripper," among others) get their moment in the spotlight, as do others involved in the investigation (Frederick Abberline, Robert J. Lees, Walter Dew, etc.). While the novel "solves" the Martha Tabram murder, the identity of Jack the Ripper remains a mystery.
I do recommend this to those who, like me, are interested in Holmes-Ripper stories, but I wouldn't put it at the top of the list.